It's not legal because that is a specific style used by lawyers (although in some cases sporting rules might be written that way), but otherwise it is a similar genre. In fact, sporting rules might be very similar to a contract (possibly sometimes even legally binding, regarding for example payment).

I'd call all of them regulations. And what varies is domain: whether they're enforced by the government, by scientists, by employers, or in this case by whatever organizers the sport has.